Billing system for computer software

ABSTRACT

A computer software security and billing system is disclosed in which the application program is enciphered in accordance with an algorithm driven by a numeric key. The user&#39;s computer is provided with a hardware security module and a removable billing module, both of which carry unique codes. A security program accesses the application program and also writes information about billing into the billing module. The billing module is periodically replaced so the user can be charged based on amount of usage of the software.

This is a continuation-in-part of patent application Ser. No. 922,689filed Oct. 24, 1986, now U.S. Pat. No. 4,796,181.

FIELD OF THE INVENTION

The present invention relates to the field of the marketing of computersoftware in general, and relates, in particular, to a system forsecuring and/or encoding personal computer software so that it can bemarketed to the ultimate user on a pay-per-usage arrangement rather thanon a fixed fee purchase price.

BACKGROUND OF THE INVENTION

The personal computer industry has grown enormously in the past decadeand has created a large market in software suitable for operation ofpersonal computers. Many companies are in the business of creating andpublishing computer software packages which are then marketed topersonal computer owners for use in their machines. Typically suchcomputer software packages are marketed on a fixed fee basis in which auser purchases a copy of the software, usually under terms of a writtenlicense, for a fixed price thereby granting to the user perpetual use ofthe software. It has been a characteristic of this industry that inorder for the publishers of the software to recover the often quitelarge investment in research and development of the software, and alsothe costs of manufacture and marketing, that the purchase price of manysuch software items has been relatively high, particularly for limiteddistribution or special-purpose software. This high purchase price hasbeen a barrier, in some circumstances, to the widespread sale of somesoftware and has limited the penetration of software publishers in somemarkets. In addition, some users are reluctant to incur such a purchaseprice without first operating the software, since the suitability ofsoftware is very difficult to judge without actually using it.

The relatively high purchase price of software has lead to anotherphenomenon perceived as a problem by many software publishers. It isoften relatively easy for a personal computer owner to make duplicatecopies of any software which the owner has purchased unless the softwareis in some fashion protected from such copying. It has become quitecommon for some personal computer owners to make and disseminate suchcopies to their friends and acquaintances. This often widespreadunauthorized copying dilutes the market for the software product and maycause the publisher to ask even a higher price for each legitimate copyof the product in order to ensure a reasonable amount of return.

One solution to this dilemma has been for manufacturers to institutecopy protection schemes which are intended to allow media carryingpersonal computer software to be sold with the media containingtechnical devices intended to ensure that unauthorized copies cannot bemade on personal computers. Copy protection schemes were put into placeby a variety of companies using various techniques. One technique was touse a non-standard format for the magnetic disk on which the program wasstored, with the non-standard format not being copyable given theoperating system for the personal computer for which the program wasintended. A second technique which was used was to introduce limitedformat error or an altered physical characteristic into the disk whichthe computer is unable to duplicate when copying the disk. Specialcommands in the program would then check for that identifyinginformation before allowing operation of any programs on the disk andthus to ensure that the disk was not a copy. It has been a more recenttrend that a third category of software protection schemes have beenproposed which involve physical protection either by making physicalvariances in the disk which must be checked by the program before it canoperate or by requiring hardware devices, known as "locks," which mustbe purchased along with the software in order to operate it. All suchcopy protection schemes have suffered from some disadvantages in thatthe technique of protection of many of the schemes have been deduced byindividual computer owners who then widely publish how the copyingprotection scheme may be avoided. Certain programs are also soldcommercially which enable the copying of certain disks which areotherwise intended to be copy protected. Hardware based systems can alsobe avoided by the custom creation of hardware devices which can emulatethe lock intended to be sold with the system.

It is also generally known in the prior art that computer programs canbe encrypted or encoded so that they must be used with a specialmicroprocessor or other unique hardware having the capacity to decryptor decode the program. Such systems are limited to the particularencryption/decryption system hard-wired into the computer and thus arevulnerable to unauthorized use once the methodology of the system isdeduced once by a user.

SUMMARY OF THE INVENTION

The present invention is summarized in that a billing system for thedistribution of personal computer software includes a security modulewhich may be installed in the personal computer of the user; a billingmodule which may be installed and removed from the expansion modulecontained in the computer and which contains therein suitable memorylocation for the writing and reading of billing information; and atleast two programs on a memory media deliverable to the user, oneprogram being a security program and the other program being anenciphered application program, the security program serving tointerrogate the security module and the billing module to determine thecodes therefrom, using that information to generate a decipher algorithmand using that decipher algorithm to decipher the application programwhich may then be operated by the personal computer.

It is an object of the present invention to provide a security andbilling system for personal computers which allows users to make anunlimited number of copies of the program without endangering theoverall program security or the appropriate return of income to thesoftware publisher.

It is yet another object of the present invention to provide a softwaredissemination and billing system which allows for users to obtain accessto personal computer software on a pay-per-usage basis so that softwarecan be evaluated, tested, and used without a large initial investment inthe software package while still ensuring a return of income to thesoftware creators for actual use of the software.

It is yet another object of the present invention to provide a securitysystem for software distributed in such a billing system such that thebilling system is extremely difficult to evade.

Other objects, features, and advantages of the present invention willbecome apparent from the following specification when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a schematic illustration of a billing system constructed inaccordance with the present invention.

FIG. 2 is a flow chart diagram of a method of operating a billing andsecurity system in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention disclosed herein can be conceptualized as having a minimumbasic system for software security and billing and a series ofadditional options or features which may be added thereto. Theadditional options and features on this system may either increase thedesirability of the system from a commercial viewpoint or enhance thesecurity of the system, and may be added individually or in groups tothe basic system. Some of the options and enhancements are likely to beused in an actual commercial embodiment of this invention. However, inorder to understand the concept of the present invention most fully, itis first necessary to understand what the basic core concept containedherein is. Accordingly, it is first necessary to examine the simplestpossible system constructed in accordance with the present invention.

A basic computer software security and billing system according to thepresent invention is illustrated by the block diagram of FIG. 1 as usedin a personal computer. A personal computer, having a central processingunit (CPU), resident memory, input/output interfaces, and other relatedcircuitry, is generally indicated at 10 and is otherwise conventionaland well-known in the art. The computer CPU and memory unit wouldnormally include one or more media on which computer software programscan be stored, typically a disk drive, such as that generally indicatedat 12 in FIG. 1. While the present invention is particularly describedwith regard to a conventional magnetic disk media currently as is usedin personal computers, it is to be understood that it is equallyapplicable to other permanent memory media such as magnetic cartridge,optical disk, rom chip, etc. In the embodiment of FIG. 1, theconventional disk drive 12 may be loaded with an appropriately formattedmagnetic diskette 14 containing thereon programs to be utilized by theuser. The diskette 14 is a conventional diskette in its physicalmake-up, although the programs carried on it will be somewhat unique aswill be discussed below. The unique hardware required by the presentsystem is a security module generally indicated at 16. The securitymodule 16 is a hard-wired logic circuit electronically attached to thepersonal computer 10. The security module 16 may be constructed as anexpansion card which can be inserted into the chassis of a personalcomputer having a so-called "open" architecture. The security module mayalso be a stand-alone accessory to the main computer which is attachedto the computer by an appropriate serial or parallel port. The method ofcommunication, i.e., whether it is parallel or serial, between the maincomputer and the security module 16 is unimportant as long as there areaddress and bi-directional data paths for information to be transferredbetween the security module 16 and the personal computer 10.

Within the security module 16 is located at least one fixed memorydevice 18, preferably a PROM or programmable read-only memory. Otherfixed memory devices than a PROM may also be used within the scope ofthe present invention as long as the device used is capable of holdingfixed numerical information of the type required here. The PROM 18 inthe security module carries thereon a fixed pre-selected numerical code,referred to here as an internal code. The internal code is unique toeach individual security module 16. The security module 16 also maycarry elsewhere there on it a serial number also unique to the securitymodule 16. The serial number on the security module 16, which is usuallynot the same in numerical value as the internal code carried in thePROM, is preferably fixed in both electrical form (such as in a PROM orswitch settings) and in human readable form so that security modules 16can be matched with appropriate internal codes.

Also carried on the security module 16, when it is in use, is a billingmodule 20. The billing module 20 is a removable memory device which canbe inserted into a previously provided access interface on the securitymodule 16. In other words, the billing module 20 is a removable memorymodule which can be easily removed from and inserted into the securitymodule 16. The billing module 16 must have a memory portion which can beread by the computer 10 through the security module and written thereon.Accordingly, the exact media of the billing module can be varied withinthe scope of the present invention. Many media can be used for thebilling module 20 based on magnetic, electronic, optical or evenphysical data storage technologies. A suitable medium might include apaper card having a magnetic memory portion thereon which can beinserted in a read/write interface provided on the security module 16.For example, the security module 16 could be a stand-alone accessory toa personal computer and could have a simple card slot into which a papercard carrying a magnetic strip thereon is inserted with the magneticstrip serving as the billing module 20. It is the preferred embodimentof the billing module in the present invention, however, that thebilling module 20 consist of an EEPROM. An EEPROM is an electricallyalterable and erasable programmable read only memory. Preferably theEEPROM billing module 20 is encapsulized in such a fashion that it iseasy to handle by a user and is designed to interface with a simplemechanical and electrical interface provided on the security module 16into which the billing module 20 can be inserted.

While the billing module may often be removable, it is also envisionedthat in some variations, the billing module might not be removable. Inone such variation, the billing module could be connected through amodem to be updated and read for billing purposes by telephone. Anotherpossibility is that the billing module could be connected to appropriatecircuitry to be updated by fixed wire or by radio signal. It is alsopossible for the billing module to be located some distance from thecomputer, for example at a different station in a local area networkwhere it could be polled and updated as needed and could be used by anumber of personal computers.

The billing module 20, of whatever media it is contructed, has at leasttwo portions of memory thereon. The first memory portion carries anumerical value referred to here as an external code. The second portionof the billing module memory consists of billing memory. The externalcode is a number designed by the computer to be read from the billingmodule 20. There may be more than one external code and the externalcode may consist of more than one portion or part. The billing memory isintended to store billing information which may be data previouslyloaded onto the billing module 20 or may be a blank area on the billingmodule 20 onto which information may be written. In either event, it iscritical to the present invention that the billing memory portion of thebilling module 20 be alterable by the computer 10 in accordance withinformation received and processed by it. It is therefore also possiblethat the billing module itself could be embodied in a removable magneticstorage media, such as a floppy diskette, which could have an area ontowhich the external code was pre-recorded and a separate portion intowhich billing information is loaded.

The application diskette 14 for use within the present invention carriesthereon at least one computer program which the user desires to operate.This is referred to herein as the "application" program. In accordancewith the present invention, the application program is enciphered inaccordance with an algorithm driven by a numerical key, as will bediscussed in more detail. The diskette 14 therefore carries theapplication program in its enciphered form. The diskette 14 also carriesan unenciphered start program. In addition, the diskette 14 also carriesa security program which may or may not be enciphered depending on thelevel of redundant security desired in the embodiment of the presentinvention. If the security program is not enciphered, then the startprogram may merely be a portion of the security program.

In its operation, the basic system illustrated in FIG. 1 is intended tooperate as follows. The computer 10 is operated in a normal fashion andthe diskette 14 carrying the enciphered application program which theuser desires to operate is loaded into the computer disk drive 12. As isconventional, the computer CPU loads the program from a previouslydesignated portion of the diskette 14. Carried on that previouslydesignated portion of the diskette 14 is the unenciphered start programwhich is thus loaded into the resident memory in the computer 10. Thestart program then operates. In its most basic embodiment, the firstthing that the start program does is verify the presence of the securitymodule carrying an active billing module in it. The start program alsoverifies from the billing module that the user still has billing creditto operate the program before it will proceed. Assuming that the billingmodule is present, and billing credit is available to the user, thesecurity program is run. The security program reads the external codefrom the billing module 20. This code serves as a "key" to a previouslyselected algorithm utilized by the security program. No singleparticular algorithm is to be used for the enciphering and decipheringof all application programs. In fact, it is intended that differentalgorithms be used on different diskettes 14, as long as the securityprogram on any diskette corresponds to the algorithm used to encipherthe application program on the diskette. Each algorithm so used ispreferably based on a numeric key so that the same key must be availableto decipher the program as was used to encipher it, although it wouldalso be possible to use a two key system in which the encoding key isdifferent from the decoding key. Thus the algorithm used by the securityprogram is the inverse of the algorithm used to encipher the applicationprogram. The security program uses the key from the external code tooperate a deciphering algorithm to decipher the enciphered applicationprogram. The security program may decipher the entire applicationprogram, or may only decipher one or more modules of the applicationprogram which are to be used by the user at one time, or may decipheronly a small number of very important program instructions addresses orlocations. The security program may also shift a small number ofmislocated instructions. The security program then turns over executionto the application program which thereby proceeds to execute for theuser.

As the application program executes, the security program periodicallymonitors application program execution. This can be done by formattingthe application program as a routine called by the security program withprogram execution periodically returned to the security program oralternatively may be accomplished through one or more interrupts bywhich the security program interrupts operation of the applicationprogram. In any event, during this periodic process, the securityprogram verifies continued use of the application program within thecomputer, and assuming that use is continuing, the security program thencreates billing data based on program usage. The billing data is storedon the diskette 14 at very frequent intervals and is then periodicallywritten into the billing information area of the billing module 20.There are generally two approaches for entering billing information inthe billing module 20. In one approach, the billing memory of thebilling module 20 is provided with a pre-established authorization of acertain amount which is loaded into the billing memory of the billingmodule 20 before it is supplied to the user. In this variation, thesecurity program would then decrease, or decrement, the value of thebilling credit authorization contained in the billing memory as use ofthe application program continued. In the second approach in whichcredit is extended to the user, the security program would note when theapplication program execution continues, and write information onto thebilling memory indicating usage by the user. This approach would be toincrement the billing memory by adding additional information thereto.Regardless of whether a decremental or incremental system is usedconveying billing information to the billing memory, the billing can bedone on a time basis or can alternatively be done by monitoring any typeof operation by the application program, such as disk access orreloading of different modules, which is generally indicative of theamount of use of the application program which is being enjoyed by theuser.

This system, in its simplest variation as described, conditions theusers access to the application program on the presence of a properlymatched billing module 20 which must also have billing authorization onit. The billing module 20 must be matched to the diskette 14 in thesense that the application program on the diskette is encoded by analgorithm the key to which is derived from the external code on thebilling module 20. The numeric decipher key is thus unique to the user,although the encipher/decipher algorithm may vary from diskette todiskette. This system is the easiest to implement and maintain. Userscould return the billing module 20, usually by mail to the dealer orbilling center for additional usage authorization when the limit set inthe billing module 20 is reached. Alternatively, the billing modules 20could be read and reloaded via modern hook-up. Thus users could becharged only for the usage they make of the software. In addition, sincethe codes can be changed periodically, permanent breach of the securityof the system is unlikely.

The first level of additional sophistication and security to be added tothis basic system is to make use of the internal code in the PROM 18 inthe security module. The decipher key used in the algorithm by thesecurity program would then not be simply derived from the external codebut would be derived from both the internal and external codes. Thisderivation of the decipher key could be relatively simple, such assimple addition of the internal and external codes, or could also be amore complex relationship. Thus the security program would first derivethe decipher key, by whatever method was selected, and then use that keyin the algorithm to decipher the application program.

The effect of this enhancement to the system is to create additionalsecurity. The user cannot evade the security of the system simply bylearning the external code. By requiring the internal and external codesto be combined, the chances of a user gaining access to both codes isreduced and the system is very difficult to crack. Furthermore transferof the billing module to an unauthorized computer is prevented.

These simplest and most basic variations in this system providessignificant security to the software creator and distributor. Theexternal code and internal code are unique to any individual user andthus the enciphered application program on the diskette 14 may only besuccessfully used by the single user who has validly obtained a securitymodule 16 and an appropriate billing module 20 for use with thatspecific individual security module 20. Thus for use with a diskette 14it is not required that any form of copy protection be employed, sincethe user can make simply as many copies as he may desire. Each of thesecopies will be useless to the user, however, unless it is used inconjunction with the security module 16 containing an appropriatebilling module 20 therein. Extra copies of the enciphered applicationprogram will not allow the user to run the program and there istherefore no benefit to him. The security of the system is inherentlydifficult to break because of the fact that the internal code in thePROM 18 in the security module and in the external code of the billingmodule 20 are previously selected and unique to each individualcomputer. Therefore if one user of software distributed in this fashionshould uncover the algorithm used by a particular security program, andthe internal and external codes used with a particular security module16 and billing module 20 for a program that he has in his possesion,that information will not be sufficient for another user to evade systemsecurity since the code will be different. In addition, various versionsof the security program can be used, each utilizing a differentalgorithm for the enciphering and deciphering process. In this way,multiple levels of security are provided without the necessity for copyprotection.

An additional method for monitoring any non-compliance with the securityfeatures of the system of the presence is to individualize eachlegitimately sold diskette 14. The diskettes 14 could be provided withindividual hidden serial numbers or with individualized non-functionalprogram-like character sequences. If this option is used, and thesecurity is breached, at least the breach can be traced back to thediskette from which non-secure copies were made to facilitate remedialaction.

In addition, users can be billed on a charge per-use basis in any easyfashion. Using a decremental billing system, the user can purchase abilling module 20 from his software supplier containing apre-authorization of a certain amount of usage. He then takes thebilling module 20 home, and takes the program disk 14 enciphered tomatch his billing module 20 home with him and operates the program as hedesires. If the user exceeds the amount of authorization contained inthe billing module, program execution stops. If the user decides herequires no further use of the program, he returns it to his vendor andis given credit for the remaining authorization contained in the billingmodule which he returns to his dealer. Alternatively, for customers whoare creditworthy, the billing modules can be issued to them on a creditbasis. Again a specific billing module 20 has to match a diskettecontaining an application program enciphered by an algorithm whosedecipher key matches the external code in the billing module 20. Theuser can take the program home, operate it as desired, and returning thebilling module periodically to the supplier for reading. The suppliercan then bill the user for his use. Under such a system, the billingmodule would be replaced periodically by the supplier, typically on somekind of fixed time period basis, such as monthly. The transaction couldoccur by mail, particularly if the billing module consists of an EEPROM,which can easily be mailed to the supplier and back to the user eachmonth, so that the user always has a billing module operable in hissystem. Another alternative is for the billing module to be readremotely by a billing facility. A modem and suitable software couldallow the computer 10 to be remotely accessed by telephone so that thecentral facility could read billing information on the billing module 20to charge the user.

As can be seen from the foregoing discussion, the present invention isnot dependent on any particular algorithm. In fact the system isoperable with quite a variation in the type of algorithm used for theencrypting as long as the appropriately encrypted algorithm is used withthe appropriate de-encrypting security program on the disk and furtheras long as the encryption and decryption are keyed by the same numerickey. Since the disk is supplied with both the enciphered applicationprogram and the security program intended to do the de-enciphering, theinformation actually physically in the computer, consisting of the codesand billing information in the billing module and on the security moduleis, in essence, independent of the encryption algorithm used on theprogram which is used with it.

To better understand the present invention it is helpful to consider anexample of a simple method for deciphering an application program. Thissimple example uses relatively short codes. In practice, a more complexalgorithm methodology and longer codes would be used to add to systemsecurity.

As is made clear from the discussion above, the enciphering ordeciphering procedure of the present invention is driven by a numericalcode, referred to as the decipher key. The enciphering key is chosen atrandom and used in the algorithm to create the enciphered program.Therefore the first step in the deciphering procedure is to derive orcreate the appropriate deciphering key corresponding to the encipheringkey used for the program in question. To develop the deciphering key,the security program would read the code contained in the billing module20 of the security module 16, known as the external code. This externalcode would then be added to the internal code contained in the PROM 18permanently mounted in the security module 16. These two codes wouldalso be operated on by the disk code which would be resident on theapplications diskette 14 which is desired to be operated by the system.Since the enciphering key was chosen at random, and since the internalcode contained in the security module 16 is fixed, the external codecontained in the billing module 20 and the disk code contained in thediskette 14 must be properly selected so that the operation of thealgorithm on all these codes yields the appropriate deciphering key. Inthe example here, where the algorithm consists of simple addition, thethree codes may simply be added through normal binary addition asfollows.

    ______________________________________                                        External Code           1010                                                  Internal Code           1001                                                  Disk Code             +10110                                                  Deciphering Key        101001                                                 ______________________________________                                    

This step yields a numerical value for the deciphering key which thenmay be used as the key to the deciphering algorithm. Obviously thelength of the codes may vary from application to application and thesize of the various three code components may also vary with respect toeach other.

Once the deciphering key has been derived using this procedure, thedeciphering key may then be used to decipher the program in segments.The deciphering key is used repetitively and applied to the encipheredprogram code in a method determined by the algorithm. Again, forpurposes of this discussion, we will assume that the algorithm ofdeciphering is simple repetitive logical addition of the deciphering keyto the bits of the enciphered program text. That procedure would proceedas follows:

    ______________________________________                                        Enciphered Program Text                                                                           101110    010101                                          Repeating Deciphering Key                                                                         +1010001  101001                                          Deciphered Program Text                                                                           [1]010111 111110                                          ______________________________________                                    

The numeral in brackets above, [1], is the carry-forward.

The deciphered program text would be loaded into a portion of computermemory to which operation of the program can be transfered in anappropriate step in the security program. The deciphered applicationprogram text would constitute the actual instructions to be operated bythe computer during the application program. For the above simpledeciphering procedure, the enciphering program would be the reverseprocedure in which the enciphering key would be subtracted from theunenciphered program text to create the enciphered program text.

In one variation of the procedure of the present invention, it may bedesirable to add additional security by enciphering the disk code aswell. If this was done, the codes from the internal and external codeswould first be added to create a code that would be used as a key indeciphering the disk code itself. Then the disk code would be added tothe internal and external codes to create the deciphering key for theprogram text itself.

It is also possible that certain important numbers to the operation ofthe software, such as program addresses or the locations of certainprogram instructions within the address itself, or as to the relativelocation of information on certain sectors of the floppy disk, may beindividually enciphered. In fact, if such addresses are contained withinthe text of the actual program itself, it may be possible to encipherthem within the plain program text and then encipher the entire programtext so that those particular key addresses or location numbers aredoubly enciphered. To decipher such doubly enciphered numbers wouldsimply be the reverse procedure in which the entire program text isfirst deciphered and then individual predetermined key addresses orlocation numbers would then be de-enciphered.

Within this general scheme, the algorithms both for generating thedeciphering key and for deciphering the program text can be variedenormously. While arithmetic or algebraic algorithms are preferred,other algorithms of varying degrees of simplicity or complexity can alsobe utilized. For example, in creating the deciphering key, rather thanadding the various codes together, they could be placed sequentially inbinary fashion to create a long numerical value which could be used asthe deciphering key. The algorithm for deciphering the program textcould involve shifting of data by bit position, or in predetermined unitsizes which may or may not correspond to standard byte lengthinstructions, as long as the methodology and timing of the shifts ofdata is consistent in such a fashion such that deciphering isappropriately available. In other words, the term "deciphering" as usedhere is not limited just to encoding of letters, terms or charactersequences, but refers to any rearrangement of the application program,or its code, which prevents effective operation of the program in itsenciphered form, which is based on an enciphering and deciphering key,and which is reliably decipherable with the key. For example, it ispossible to have enciphering routines which would call for therelocation or rotation of various code or instruction sequences aroundthe program. It is also possible that program segments could bedistributed around the diskette 14 in such a fashion that the segmentshave to be re-ordered to function, and the method of this reordering canbe determined by such an algorithm. Again, all these variations wouldhave to be done in a methodology that is consistent so that thedeciphering program could unscramble the disrupted sequence ofinstructions to properly read and execute the application's program.

Shown in FIG. 2 is a flow chart generally illustrating the proceduralsteps which would have to be followed by the start program and thesecurity program to properly operate an application program inaccordance with the present invention. The start program and thesecurity program can be considered as one program if the securityprogram is unenciphered. In some variations of the present invention itmay be desirable to encipher the security program which is thendeciphered by the start program. For purposes of this illustration, thesecurity program will be unenciphered and the two programs will bereferred to together, as they are illustrated as one flow-chart in FIG.2. The program is first loaded from the disk and that program beginswith a step of reading the startup instructions as indicated byreference numeral 22. The program then performs a series anti-demontests as indicated by program step number 24. A demon is a program orhardware implemented in a personal computer to watch for tests of copyprotection identification and then to provide simulated properidentification response, even if the program is an illegal copy. Demonsare generally placed in RAM memory although theoretically it is possibleto create such demons resident in an interal ROM memory. This programstep 24 is simply intended to test for the presence of those devices soas to avoid them or avoid operation in their presence as appropriate.Step number 26 in the operation of the program is to read informationfrom the PROM 18 located on the security module 16. This informationwould include the internal code carried on the PROM 18 and might alsoinclude the hard-wired serial number carried on the security module 16.The information read from the PROM is then utilized to generate a latchcode to be presented to the EEPROM which is the billing module 20. It ispreferred that the EEPROM billing module 20 have a latch mechanismwhereby a proper latch code must be presented to the EEPROM 20 to gainaccess to it, and this step is to generate that code. Program stepnumber 28 indicates that this calculation occurs and that the latch codeis presented to the EEPROM to enable reading and writing on the EEPROM.The first step in reading from the EEPROM occurs at step number 30 wherean update check is made as to billing memory locations within thebilling module 20 itself. The update check 30, a system option, wouldhave the program examine predetermined locations in billing module 20memory to see the current update, or release, status of the software.Because the application program, or the security program, may be updatedperiodically, and because the billing module 20 is periodicallyreplaced, information placed in the billing module 20 about updates inthe application program can be read at this point. The updateinformation can be used to inform the user or to prevent further systemoperation if the supplier wants to ensure all program copies areupdated. In other words the systems program would stop execution of theprogram if the information on the billing module indicates that thisversion of the security program is obsolete. At step number 32, theappropriate billing authorization information is read from the EEPROM ofthe billing module 20 so that the program can evaluate the billinginformation. At decisional step number 34 the billing authorizationinformation obtained from the billing module 20 is analyzed to determineif the billing module is full or if the credit limit has been exceeded.If either condition is true such that there is no longer sufficientauthorization to the user to utilize the application program, then theprogram proceeds directly to a stop at 36. If the billing module stillcontains current credit or authorization for the user's use of theapplication program, then the process can proceed. The next step 40commences a procedure which is more logically a part of the securityprogram if it is separate from the start program, although the boundarybetween the two can be to some degree definitional. The program whichhas now gained access to the EEPROM billing module 20 reads from theEEPROM the external code or codes to be utilized in the decipheringalgorithm. At the next step 42 the program uses the internal andexternal codes, together with the disk code read from the diskette 14,to generate the decipher key. The decipher key, as referred to earlier,is a numeric value to be used as the key in the enciphering anddeciphering algorithm for the application program. The program thenproceeds to step 44 wherein the key is implemented in the decipheringand locating algorithm. The algorithm is operative both to deciphersegments of program code so as to create plain unenciphered computerprogram text out of enciphered text, and may also be used as a locatingmechanism to unscramble various program segments placed in a scrambledfashion in various locations on the diskette 14. The program thenproceeds in step 44 to decipher the various program sectors and assemblein RAM the resulting deciphered program text in its proper order forproper execution of the application program.

It is also possible that within the actual deciphered applicationprogram there may have been deliberately mislocated instructions as partof the enciphering and security process in creating the encipheredapplication program. If this option is used within the structure of thepresent system, the location and relocation of those mislocatedinstructions is determined by the internal and external codes which areagain utilized to generate a key which determines the placement of themisplaced program instructions. If this option is utilized within thepresent invention, a program step 48 is then necessary at this point torelocate any such mislocated instructions and to relocate them in properfashion in resident memory so that the application program can properlyexecute. Also as an additional optional security feature within thepresent invention, the program would remove disable instructions and addcopy prevent instructions to the operating system or other residentinstructions contained in the personal computer to prevent disruption ofthe operation of the application program in any manner which is notintended. A related procedure may be implemented at 52 in which copy orinterrupt commands are evaluated to determine if they are appropriate ornot. If step 52 is implemented, then each copy or interrupt command isevaluated to determine whether or not it is appropriate, as a logicalstep 54, and if it is determined that a command is inappropriate, thenthe program stops executing at 56.

If the user does operate the system correctly, the application programwould then execute. While the application program is executing, it isstill necessary for the security program to maintain overall control ofthe program execution and to monitor its execution. This securityprogram would, as indicated by step 58, measure usage of the applicationprogram. This measurement could be done by simple counting time ofoperation of the application program or alternatively could be donethrough measurement of certain loops through program operation ormeasurement of the number of calculations performed, depending on thebilling strategy of the application program publisher and on the purposeof application program itself. At periodic intervals, when it isdetermined that an appropriate billing milestone has been passed, thesecurity program would then proceed to step 60 at which it would writeapplication program usage information on the diskette 14 on which theapplication program is carried. This writing of billing information ontothe diskette, or hard disk if a hard disk is utilized, should be donerelatively frequently, perhaps every thirty seconds or once a minute. Atthe same time, it is preferable that the previous written number couldbe read and compared to records resident in memory to ensure that therehas been no alternation of the billing sequence such as might occur ifthe computer was turned off or if an attempt was made to alter thebilling information on the system. At a longer periodic basis, perhapsat intervals of fifteen minutes to a half hour of elapsed time, thesecurity program would then have to write billing information onto thebilling module 20 itself at step 62. This information could be done intwo ways. If the billing module receives additive information, then theprogram would write affirmative data onto the billing module in thebilling memory portion thereof. If the billing module is provided with apre-set amount of authorization, then at step 62 a subtraction from thatauthorization would be made leaving a new balance which represents theremaining credit allowable to the user. The program would then test forbilling authority to determine that there is still sufficient billingauthority in the billing module for the user to proceed. If not theprogram would immediately stop. If the billing authority does exist,then execution of the program could proceed until terminated by theuser.

It may be desirable to enhance the security of the transfer of datarelating to usage. If this is desired, when the usage data is incomputer RAM memory a check sum is generated from the usage data andboth the usage data and the check sum are encoded. The encoded numbersare then written to disk. Data transfer between the disk and the billingmodule can be similarly protected by encoding.

It may also be desirable to have additional anti-demon tests or othertests for security evasion located at various parts of the securityprogram to ensure that deception of the overall security operation ofthe system is not impaired.

Another option within the present system is to insert validationnumbers, which would be sequential or encoded numerical values, whichcould be written by the system from the billing module or onto thediskette 14. The system would then always check to make sure that aproper validation number is resident in the billing module at varioustimes in the program to ensure that no unauthorized interruption of thesystem has occurred or improper usage thereof. For example, each billingmodule might contain a validation number which can be derived from thenext-precedent validation number. In this way, if the system tests foreither the same or next validation number, use of an unauthorizedbilling module is prevented, although this level of security may be seenas redundant. Alternatively, the validation number could be generatedfrom a measure of program usage to ensure that the billing module ischanged periodically. The most preferred method for the validationnumber to function is that the validation number, in enciphered form,would be transferred from the billing module to the disk containing theapplication program. When the billing module is changed, a validationkey is read from the new billing module and used to decipher theenciphered validation number from the previous billing module. Thedeciphered validation number is compared to the expected value beforeapplication program execution can proceed. Other similar variations andmodifications are possible within the scope of the present invention toadd further redundant security to the system.

For example, in another, more sophisticated, version of the presentinvention the security module itself could be provided with a securitymodule microprocessor connected directly both to the PROM in thesecurity module and the EEPROM in the billing module. The securitymodule microprocessor is capable of enciphering and deciphering datatransfers between the billing module and the main microprocessor or thedisk. The security module microprocessor would generate the decipheringkey, through a unique routine carried in either the PROM in the securitymodule or in the billing module. The program usage or billinginformation would also be transferred directly to the security modulemicroprocessor where it is accumulated for periodic transfer to thebilling module.

An enhancement of this microprocessor-equipped security module would bethat this security module could service more than one personal computer.For large organizations, such as corporations, with many personalcomputers connected in a local-area-network, or LAN, it would bepossible for a single processor, designated a billing concentrator, topoll the billing modules of the computers on the network to read off thebilling information from each node in the system. The billingconcentrator would communicate billing information, perhaps by modem,with the central billing authority. For this option to be effective,microprocessors are necessary in the security modules to be able tocommunicate with the billing concentrator.

It is understood that the invention is not confined to the particularconstruction and arrangement of parts herein illustrated and described,but embraces such modified forms thereof as come within the scope of thefollowing claims.

I claim:
 1. A billing system for billing users on a usage basis for anenciphered application software program for a computer comprising:ahardware security module attached to the computer, the security modulecarrying therein a fixed computer-readable numeric internal code andalso carrying a billing module interface; a billing module electricallyconnected to the security module and electrically connecting to thebilling module interface therein, the billing module having fixed andalterable memory therein with a fixed computer-readable numeric externalcode in the fixed memory and billing information stored in the alterablememory, and a storage medium for the computer carrying an encipheredapplication program thereon and also carrying thereon security programmeans for (1) causing the computer to read the internal code and theexternal code, (2) using the internal and external codes to generate adecipher key which is used in a predetermined algorithm to decipher theapplication program for use by the user, and (3) writing usage billinginformation in the alterable memory in the billing module.
 2. A billingsystem as claimed in claim 1 wherein the security program means readsbilling authorization information from the billing module beforedeciphering the application program and wherein the security programmeans will not decipher the application program if the billingauthorization is insufficient.
 3. A billing system as claimed in claim 2wherein a pre-established billing authorization amount is stored in thebilling module and the security program means writes usage billinginformation in the billing module by decrementing the authorizationamount based on usage.
 4. A billing system as claimed in claim 2 whereina pre-established authorization limit on the amount of memory of thebilling memory set aside for billing information is established andwherein the security program means writes billing information in thatmemory until the authorization limit is reached.
 5. A billing system asclaimed in claim 1 wherein the security module includes both residentread-only memory and the microprocessor, the security module connectingto the billing module and controlling interactions and communicationsbetween the computer and the storage medium and the billing module.